An object dropped from rest from the top of a tall building on Planet X falls a distance d(t) = 201" feet in the first t seconds. Find the average rate of change of distance with respect to time as t changes from t, = 4 to to = 9. This rate is known as the average velocity, or speed reet The average velocity as t changes from 4 to 9 seconds is- sec (Simplify your answer.)